Leigh Griffiths becomes the first Celtic player since Henrik Larsson to score 40 goals in a season

Bailly was busy enough in the early exchanges as St Johnstone found a lot of joy down their right, where Emilio Izaguirre was playing what might prove to be his last game for the champions given Tierney's form.

The goalkeeper had a few testing crosses to deal with in the first few minutes but it was Saints' last line of defence that kept the scoreline level when the visitors finally clicked going forward.

Clark denied Griffiths with a fine save just when Scotland's top marksman seemed certain to convert an inviting cross following intelligent set-up play from Christie.

That was a rare moment of anxiety for Tommy Wright's side as they dominated possession for long spells of the first half as Celtic found it hard to produce any fluent attacking football.

Their increased tempo early in the second paid off with another sublime goal from Griffiths.

There seemed little danger when he picked up possession at the left edge of box but he weaved past two challenges before stabbing a left-foot shot beyond the onrushing Clark, his 31st league goal.

St Johnstone were gifted the chance of a quick equaliser in the 55th minute when Johansen was caught in possession on the edge of his own penalty area and veteran striker MacLean finished with aplomb.

The game looked to be drifting towards a draw before Ambrose tangled with Bailly and Cummins tapped home to make it four straight post-split wins for Tommy Wright's side.